Incandescent lamp filament

ABSTRACT

In order to prevent a short lifetime of a lamp experiencing an extending downward of the coil under application stress when the coil is in a vertical configuration, there is provided an incandescent lamp in which a filament is stored in a bulb, and the filament is arranged in a vertical orientation and held by supporting element, where the filament is composed of a double coil in which a primary coil having a strand wound thereon is doubly wound, and the primary coil is more closely wound at the upper part of the filament than at the lower part of the filament.

TECHNICAL FIELD

This invention relates to an incandescent lamp that is turned on with acoil axis of a filament being directed in a vertical direction, and, forexample, an incandescent lamp filled with an inert gas containinghalogen.

BACKGROUND ART

In recent years, the range of utilization of incandescent lamps actingas a heat source as well as a light source for a general illuminationpurposes and for an optical equipment and the like has expanded, andincandescent lamps have been used in a heating device for heat treatmentsuch as rapid heating, high temperature holding and rapid cooling or thelike. In such an incandescent lamp as above, one in which a double coilis applied as a filament is preferably used.

FIG. 3 illustrates one example of a double coil type incandescent lamp.A filament 20 is formed of a double coil made such that a tungsten wireis applied as a strand, and a primary coil having this wire wound at anequal pitch is further wound into a double form at an equal pitch. Thefilament 20 is constructed such that a pair of upholding parts 30, 30′also acting as inner leads are connected to both ends of the filament,and the filament 20 is arranged in a state in which the filament isbeing hung in a hollow manner within the bulb along the axis of thebulb.

This incandescent lamp 10 was lit and used in a vertical orientation,resulting in that the coil of the filament hung down as the turn-on timeexpired, and so the incandescent lamp had the disadvantage of the doublecoil also being extended downwards and being easily deformed.

That is, the incandescent lamp as described above is made such that thefilament is oriented in a vertical direction, i.e. an axis of the doublecoil is oriented in a vertical direction and the net-weight of the coilcan be set equated with stress, so that the incandescent lamp has thefeature of the load applied to the coil being lowest at the lower end ofthe filament and having a maximum at the upper end where it is graduallyincreased as the load is directed more upwardly compared with the lowerend thereof.

Due to this fact, although the stress is scarcely generated at the lowerend of the filament and prevents the coil from hanging out, the load isincreased in a more upward position from the lower end, resulting inthat the coil remarkably hangs down, and the largest extension of thecoil is found at the upper end of the filament.

In case of the aforesaid filament in the incandescent lamp, the upperend and the lower end thereof are connected to the upholding parts andfixed there so that the number of turns of the double coil and thelength of the filament do not change. Accordingly, due to the aforesaidreasons, when the coil hangs down, the pitch of the double coil isgradually narrowed toward the lower part, finally resulting in that thepitch becomes zero and the adjoining upper primary coil and lowerprimary coil of the double coil get in contact with each other and ashort-circuit state or melt-cut state of the filament and the likeoccur.

In particular, in case the incandescent lamp was used under such a hightemperature as one in which the temperature of the filament was 2600°C., for example, and its turning-on or turning-off was repeated within ashort period of time to light it in a pulse-like manner, a hang-down ofthe coil occurred remarkably, resulting in the problem of a shortlifetime of the lamp.

In view of the aforesaid circumstances, the upholding parts were fixedto not only the upper end and the lower end of the filament but alsoover its longitudinal direction, and it was possible to provide meansfor preventing a hang-down of the coil. However, in accordance with thismethod, the structure of the filament portion becomes complicated andits productivity becomes inferior.

Further, there is the circumstance that if the incandescent lamp isutilized as a heat source, in particular, when the filament length isapproximately the same as the diameter of the double coil, thearrangement of many upholding parts at the filament light emittingsection is not preferable due to the fact that the thermal efficiency ofthe lamp is reduced by this arrangement.

In view of the foregoing, it is an object of the present invention toprevent the lifetime of an incandescent lamp from being reduced due tothe coil hanging down while using a simple construction and to providean incandescent lamp having a long lifetime in use.

DISCLOSURE OF INVENTION

This invention provides an incandescent lamp in which a filament isstored in a bulb and the filament is held by upholding parts while beingoriented in a vertical direction, characterized in that the filament iscomprised of a double coil in which a primary coil having a strand woundtherein is wound in a double form and the primary coil is more closelywound at the upper part of the filament as compared with that of thelower part of the filament.

With such an arrangement as above, since the shearing stress applied tothe coil is reduced when a load is applied to the double coil,resistance against a hang-down characteristic of the coil at the upperpart of the filament is increased, the double coil hardly hangs out evenif the load applied to it is high, resulting in that a deformation ofthe filament can be prevented and it becomes possible to prevent thecoils from getting in contact with each other. Further, in accordancewith the present invention, it becomes possible to restrict thehang-down of the coil and to obtain a long lifetime of the lamp by asimple construction without changing the other configuration of the lampexcept for the filament.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view showing an example of a preferredincandescent lamp of the present invention.

FIGS. 2(a) and 2(b) are enlarged illustrations showing the coil of FIG.1 in more detail, wherein FIG. 2(a) is a side enlarged view of theprimary coil and FIG. 2(b) is a side enlarged view of the double coil.

FIG. 3 is a sectional view showing a prior art double-coil typeincandescent lamp.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the accompanying drawings, one preferred embodiment ofthe present invention will be described as follows.

FIG. 1 is an illustrative sectional view showing an incandescent lamp ofthe preferred embodiment of the present invention. In FIG. 1, theincandescent lamp 10 is a so-called one end sealed type halogen lampconstructed such that a double-coil type filament 20 is arranged insidea glass bulb 11, inert gas containing halogen is filled therein and atthe same time a sealing part 12 is formed at one end of the bulb 11 anda tip part 13 of a residual evacuation tube is formed at the other endof the bulb.

This incandescent lamp 10 is made such that when the lamp is actuallyused, a ceramic base, although not shown, for example, is installed atthe sealing part 12, the lamp is held in a vertical orientation with thebase being placed upward, and then the lamp is lit.

Upholding parts 30, 30′ acting as inner lead wires are connected to bothends of the filament 20. The upholding parts 30, 30′ are connected tomolybdenum foils 31, 31′ embedded in the sealing part 12. The molybdenumfoils 31, 31′ are connected to outer lead rods 32, 32′ projecting out ofthe sealing part 12.

The double coil 22 constituting the filament 20 is made such that atungsten wire with a filament strand, for example, is wound into adiameter of φ 1.0 to form a primary coil 21, and then this primary coilis wound a second time with a coil diameter of φ=4.8. This coil isapplied in its use with a filament length of about 9.8 mm and with anumber of turns of 6 to 7 as the number of windings, for example.

Referring next to FIG. 2(a) and FIG. 2(b), the constitution of the coilwill be described as follows. The primary coil 21 is wound such that itspitch is 0.29 mm at the first end 211, and the pitch is increased byalways 15% of the strand every time the coil is wound subsequently byten turns, and as shown in FIG. 2(a), the primary coil is closely woundat the one end 211, its pitch is gradually increased toward the otherend 212, and further the coil is wound coarsely at the other end 212.

FIG. 2(b) shows a double coil manufactured by applying the aforesaidprimary coil 21. This double coil is wound at an equal pitch with thepitch being 1.5 mm, for example.

The double coil 22 having the aforesaid constitution is made such thateach of the upholding parts 30, 30′ is connected to one end 211 and theother end 212, wherein, as shown in FIG. 1, the double coil 22 isarranged within the bulb 11 in such a way that one end 211 of the coilis positioned at the upper side of the lamp (the side where the sealingpart 12 is present) and the other end 212 of the coil is positioned atthe lower side of the lamp.

With such an arrangement as above, since the primary coil of the doublecoil is closely wound at the filament top, resistance against thehang-down of the coil at this part is increased and the hang-down of thecoil is hardly produced even if the load applied to the filament is highas compared with that of the lower side of the filament.

In accordance with the present invention it becomes possible to increasethe resistance against the hang-down of the coil in correspondence withthe load applied to the filament by using the simple construction of theprimary coil part of the double coil being closely wound at the upperpart rather than the lower part of the filament without changing thelength of the filament or without changing the number of turns of thedouble coil as well as without changing other configurations of thelamp. Thus, it becomes possible to restrict the hang-out of the coil atthe upper part of the filament and to further prevent the coil pitch atthe lower part of the filament from being narrowed.

As a result, it is possible to prevent the upper and lower adjoiningdouble coils from getting in contact with each other, and further itbecomes possible to prevent the occurrence of a short-circuit andmelt-cut of the filament, resulting in that a long lifetime of the lampcan be extended.

Further, the present invention is constructed such that a pitch of theprimary coil constituting the double coil of the filament is displacedroughly or closely in consideration of an extension of the double coilof the filament, and other various modifications of the presentinvention can be carried out for other constitutions. For example, it isalso applicable that the double coil has no equal pitch, but the doublecoil may be displaced in an axial direction. In this case, if the pitchof the double coil at the upper side of the filament is made narrow andthe pitch of the lower side of the filament is made wide, it takes muchtime until both coils get in contact with each other due to the factthat the pitch of the double coil is wide also when the double coil atthe upper part of the filament is elongated and hangs down in a downwarddirection, resulting in that it is possible to avoid a short-circuit ofthe filament as well as it being melt cut, and a long lifetime of thelamp can be realized.

In addition, the shape of the double coil can be changed into variousshapes, and it is also possible to perform an axial displacement of thediameter of the double coil when its outer appearance is not wound in acolumn-like manner as shown in FIG. 2(b), and for example, the primarycoil is wound in such a way that the diameter of the double coil isgradually increased to make a conical double coil. Further, in case aconical double coil is used, if the one end of the double coil with asmall diameter is arranged at the upper end of the filament and in turnthe other end of the double coil with a large diameter is arranged atthe lower end of the filament, this arrangement is preferable due to thefact that a shearing stress applied to the double coil at the upper partof the filament is low and the resistance of the coil against hangingdown is increased.

Industrial Applicability

As described above, the incandescent lamp of the present invention ismade such that the primary coil of the filament comprised of a doublecoil is more closely wound at the upper part of the filament than at thelower part of the filament so that, while the lamp is of a simpleconfiguration, the resistance of the coil against it hanging out can beincreased in response to a load of the filament, resulting in that thehang-down of the filament at the upper part of the filament can berestricted and the deformation of the coil can be prevented, and so itbecomes possible to prevent a short-circuit state and a melting cut ofthe filament, and a long lifetime of the lamp can be attained.

Further, the incandescent lamp of the present invention is applied to ageneral type of incandescent lamps which is lit with a coil axis of thefilament being directed in a vertical orientation; it is useful as anincandescent lamp where a hang-down of the filament may easily beproduced in which a temperature of the filament is 2600° C. or more, forexample, and its turning-on or turning-off is repeated within a shortperiod of time at such a high temperature as above; and the presentinvention is most suitable for an incandescent lamp utilized in a rapidthermal process (RTP) in manufacturing of a semiconductor device, forexample, which is filled with an inert gas containing halogen.

What is claimed is:
 1. An incandescent lamp comprising a coil filamentassembled in a vertical orientation within a bulb, supporting elementswithin the bulb for supporting both an upper and a lower end of the coilfilament, wherein said coil filament comprises a double coil comprisinga primary coil having a strand wound thereon that is doubly wound, suchthat said doubly wound primary coil is more closely wound at the upperend of said coil filament as compared with that of the lower part ofsaid filament.
 2. An incandescent lamp as set forth in claim 1, whereinthe pitch of the doubly wound primary coil is 0.29 mm at the upper endof the coil filament and the pitch increases as the doubly wound primarycoil is wound toward the lower end of the coil filament.
 3. Anincandescent lamp as set forth in claim 2, wherein the pitch of thedoubly wound primary coil is increased by 15% for every ten primary coilwindings.
 4. An incandescent lamp as set forth in claim 1, wherein thediameter of the doubly wound primary coil of the coil filament increasesfrom the upper end of the coil filament to the lower end of the coilfilament such that the coil filament has a conical shape.